A. Chlorination of Olefin Polymers with Gaseous Chlorine
It has been proposed in U.S. Pat. No. 2,890,213 and British Pat. No. 799,952 to chlorinate solid, finely divided polyethylene, i.e., polyethylene powder wherein the individual particles have a size below 300 microns and predominantly below 80 microns, directly in the vapor phase and without the use of solvent by suspending such powder in a stream of chlorine at temperatures below 100.degree. C. wherein chlorine, in amounts of from about 30 to 65 percent of polymer weight, is substantially heterogeneously distributed along the outer surfaces of the polyethylene particles. The use of such finely divided particles is disclosed as being necessary to achieve adequate rates and amounts of chlorination. Disadvantageously, such finely divided polymer particles produce excessive dust with accompanying atmospheric pollution and explosive hazards. Fluid-bed chlorination of high pressure polyethylene of larger particle size is proposed in U.S. Pat. No. 3,547,866. British Pat. No. 1,228,922 proposes the fluid-bed chlorination of low pressure polyethylene in a mixture of gaseous chlorine and oxygen.
B. Preparation of High Bulk Density Olefin Polymers
High bulk density powders of olefin polymers are also known, e.g., British Pat. No. 960,232 which discloses the preparation of powders having a bulk density exceeding 430 grams per liter by polymerizing an olefin polymer at pressures of 1 to 30 atmospheres, preferably 2 to 4 atmospheres, in the presence of a catalyst compound of a titanium containing catalyst component and diethyl aluminum monochloride or aluminum ethyl sesquichloride.
It has not heretofore been known, however, that relatively large particle size high bulk density linear olefin polymers, i.e., polymer particles ranging from predominantly at least 300 microns to about 800 microns in size and having a bulk density of from about 22 to about 36 pounds/cubic foot, could be sufficiently chlorinated, while in a fluidized bed state, to produce olefin chlorination products which may be produced and handled in the substantial absence of atmospheric pollution and explosive hazards and which, in addition, are useful for a broad range of applications as, e.g., the preparation of flexible film and sheet materials having excellent strength and modulus properties.
C. Addition of Antimony Trioxide to Chlorinated Olefin Polymers
Chlorinated olefin polymers contaning antimony trioxide, to enhance fire retardance thereof, are also known, e.g., as described in U.S. Pat. Nos. 3,113,118 and 3,121,067 and the corresponding Canadian Pat. Nos. 667,246 and 676,195. Further, the effect of antimony oxide on the rate of dehydrochlorination of chlorinated polyethylene is discussed in the Journal of Polymer Science: Part A-1, Vol. 10, pp. 881-894 (1972).
It has not heretofore been discovered, however, which discovery represents the present invention, that compositions consisting essentially of certain high bulk density olefin polymer, the individual particles thereof being predominantly in the range of from at least about 300 to about 800 microns in size and containing from about 1 to about 20 percent by weight of chlorine chemically combined therewith in a substantial heterogeneous distribution along the polymer particle, would provide tensile impact values of at least about 20 p.s.i. as determined by ASTM Test No. D-1822-61T; or that such tensile impact values could be substantially maintained even when such polymer was admixed with fire-retarding amounts of antimony trioxide and subjected to elevated temperatures for extended periods of time.
That such discovery could not be predicted from the prior art is established by reference to the previously referred to prior art patents directed to the addition of antimony trioxide to chlorinated olefin polymers wherein the presence of the antimony trioxide is shown to be detrimental to polymer strength properties; and particularly by the referred to article from the Journal of Polymer Science: Part A-1, Vol, 10, pp. 881-894 (1972) wherein it is disclosed that the presence of antimony oxide accelerates the loss of HCl from chlorinated polyethylene, following a short initial induction period.